Descriptive Biology 89 



significance. And thus it comes to be that the whole fabric 

 of morphology, or the science of form, is a mosaic of individual 

 bits of knowledge, some greater, some less, but none of great 

 importance except when considered in relation to all the 

 others. Of what particular interest for example is the dis- 

 covery of a connecting ligament between the arteries which 

 supply the lungs and those which supply the trunk in higher 

 vertebrates, apart from the existence of a functional blood 

 vessel representing this ligament in some of their more lowly 

 aquatic cousins (the lungfishes and Amphibia) ? Or how 

 can the parts of a flower be understood without a knowledge 

 of the process of reproduction in the ferns and mosses ? 



To follow adequately the course of descriptive biology in 

 America would carry us too far afield, and into paths wherein 

 many of us perchance would not care to wander. We may 

 however trace in a few words some of the main lines of 

 morphological research, noting the discoveries to which they 

 have led and the problems which still confront us. 



Since Darwin's epoch-making work, the golden thread of 

 evolution has linked together the labors of morphologist and 

 physiologist alike, and the efforts of the former have centered 

 around the genealogies of living things. What have been the 

 lines of ascent from the one-celled animals and plants to those 

 of many cells? Are animals and plants of common ancestry 

 or do they belong to two distinct groups of living things, each 

 with its own origin? What has been the origin of the germ 

 layers and the coelome in animals, and how have those of many 

 segments become modified to those of few? How can sexual 

 be related to non-sexual forms, and hermaphroditic to those 

 of separate sex ? What is the origin of alternation of genera- 

 tions, and how has the non-sexual gained so great an ascend- 

 ency over the sexual form in higher plants? These are a few 

 of the great questions which the morphologist has to answer. 

 In this solution however he must call to his aid the experi- 

 menter, for after all observation and experiment are but two 

 phases of the same science, working together toward a common 

 end. 



All living things may be divided into the two great groups 

 of the one, and the many-celled, the Protozoa and Protophyta 

 on the one hand, and the Metazoa and Metaphyta on the 

 other. Each many-celled animal or plant begins its career 

 as a single cell, containing within itself all the possibilities 

 of the adult plant or animal. So too does the one-celled 

 organism contain the possibility of evolution into a new 

 creation of beings yet unknown. Most of these lowly creatures 

 to be sure have deviated from the straight and narrow path 



